This invention relates to a method for erecting a main boom of a truck crane, which at least consists of a telescopic boom, with a fly jib which is braced via bracing trestles and bracing rods, and with a spatial boom bracing.
Frequently, very high hoisting heights and outreaches are required. The same go beyond the working ranges of telescopic cranes. Also because of possibly disturbing edges, fly jibs are mounted on the telescopic boom in such cases. The fly jibs can achieve very great lengths, which even can extend far beyond the length of the main boom itself. Such fly jibs can consist of a luffing jib or a fixed jib. When using correspondingly long fly jibs, it is absolutely necessary to provide bracing trestles and bracing rods, which extend from the bracing trestle to the tip of the fly jib.
In the case of high disturbing edges, hoisting heights of up to 170 m are achieved. With such long boom systems, a spatial bracing regularly is used at the telescopic boom for stabilization. From DE 20 2004 017 771 U1, an eccentric attachment of the bracing to the main boom tip has already become known, which likewise is used in systems with such high hoisting heights.
At present, large telescopic cranes frequently are designed such that they can be operated with a spatial bracing. Thus, in certain operating positions (for instance when erecting the main boom into a steep position), they can only reach the highest load moments with tensioned spatial bracing. Especially this operating position frequently exists when using a boom system which consists of a main boom with attached fly jib. Without the tensioned spatial bracing, the total stability of the main boom is greatly reduced. It should be noted here that the spatial bracing exclusively extends over the main boom and a possibly existing main boom extension. The fly jib, however, is held in the luffing plane by means of bracing rods and, in the case of a particularly great length, possibly by means of additional intermediate bracings.
During assembly of such large telescopic cranes, the fly jib usually is mounted completely without the foot piece. The head piece rests on a carriage, by means of which it can roll on the ground.
On the other hand, the telescopic boom is connected with the telescopic boom extensions and the adapter pieces. The spatial bracing is mounted, but not yet tensioned. There can also be effected an eccentric attachment of the bracing rods to the outer end of the main boom in accordance with DE 20 2004 017 771 U1.
The foot piece of the fly jib and the bracing trestles are attached to the main boom. The bracing rods are deposited on the fly jib and connected with the end of the head piece of the fly jib and with a bracing trestle. The foot piece of the fly jib, the bracing trestles and the bracing rods together form a transport unit. In the bracing rods, an element is provided, which is connectable with the end of the foot piece of the fly jib. Since the connection between the bracing rods and the foot piece is required for dismantling the entire boom, this connection is present during reassembly and thus need not be made again. The foot piece of the fly jib is connected with the mounted fly jib at the upper bolting points.
To be able to subsequently insert the lower bolts, a connection between bracing trestle and foot piece of the fly jib is made via the bracing rods. By means of the associated adjusting winch, the bracing trestles can now be luffed. As a result, the foot piece is lifted, until the foot piece of the fly jib can be connected with the premounted fly jib.
Subsequently, the connection of the bracing rod with the foot piece of the fly jib is separated again and the normal connection is made from the bracing trestle to the end of the luffing jib with the bracing rods. At this time, the telescopic jib of the main boom is not yet extended to the operating length.
The main boom telescoped in now is erected into a steep position, wherein the outer end of the fly jib at the bottom rests on the carriage. For this purpose, the fly jib can swivel about the pivot points at the main boom. In this way, the moment caused by the fly jib is minimized, and the bearing friction inside the telescope advantageously is reduced. At this time, however, the outer end of the boom system is free and is not supported in any way. The entire guidance of the long boom system is performed by the main boom.
Thereupon, the main boom is telescoped out to the desired length. For this purpose, the boom tray to be telescoped must each be bolted to the telescopic cylinder. Upon telescoping out, bolting of the respective telescopic stages is effected, wherein the connection of the deploying cylinder with the telescopic stages is separated. Finally, the spatial bracing is tensioned. The boom system now reaches its maximum load capacity.
During assembly of the fly jib, the greatest load for the smallest telescopic section occurs in an approximately horizontal position. Here, the entire foot weight of the fly jib (plus the bracing trestles, telescopic boom extensions and corresponding adapter pieces) with the great lever arm (e.g. length of the telescopic boom extension plus corresponding adapter pieces and foot piece of the fly jib) rests on the cross-section of the smallest telescopic stage. Even if the same is retracted, it nevertheless forms the weakest link in the main boom. This weakest link limits the maximum admissible lengths of the boom system, especially the length of the fly jib, due to the forces and moments occurring during this mounting operation.